1. Field of the Invention
The present invention relates to the field of hybrid circuits, and more particularly to high density multichip interconnect circuits for interconnecting unpackaged integrated circuits.
2. Prior Art
Recently, considerable interest has developed in forming multi-chip modules wherein a plurality of integrated circuits in chip form are mounted on a substrate and interconnected to provide the functions of Ultra Large Scale Integration (USLI) and higher integration without the normally associated problems thereof. Such interconnecting devices, sometimes referred to as high density multi-chip interconnects (HDMI), allow the testing of individual integrated circuits before mounting, thereby eliminating the need for redundancy for suitable yields. This can allow closer connection of the functional blocks on the HDMI than could be achieved in a corresponding single chip device. It also results in a faster circuit by reducing parasitic capacitance, and can eliminate the need for on-chip line drivers sometimes required on large single chip integrated circuits because of the long interconnect lines. It reduces costs by allowing testing of the integrated circuit functional blocks and the elimination of only the bad ones before using the same in the HDMI, and of course allows one to obtain the advantages of wafer scale integration without the attendant problems thereof even in applications wherein the market volume for the product is too small to consider larger scale or wafer scale integration.
At the present time, HDMI technology is somewhat of a mix, in some ways resembling integrated circuit fabrication techniques and in other ways somewhat resembling printed circuit board fabrication techniques. By way of example, conductor line widths are beginning to approach those used in at least older integrated circuit designs, and bonding techniques used to interconnect the chips to the HDMI are those typically used in conventional integrated circuit packaging. On the other hand, the materials used for the insulative layers, typically polymers, and the number of cross-overs typically required are more similar to that found in printed circuit board fabrication, as opposed to the silicon-oxide layer and the deposited metal interconnect layer of typical integrated circuits. Because of the varied materials used and the wide range of properties thereof, such structures may encounter problems regarding adhesion between layers, and stability and reliability of the interconnect, particularly when cycled over a large temperature range such as may be encountered in various ordinary applications for such devices.
In certain other prior art applications, thin layers of polymer have been cured by the bombardment thereof with high energy electrons. Such layers typically have been of a thickness of the order of 2,000 angstroms, very much thinner than that commonly used in HDMI construction.